Channel is hidden from the channel list
N This condition is true if the currently selected channel is marked as hidden from the server's channel listing, excluding it from the listing sent in response to a Client's Channel listing > Request list action.
This property is passed with the channel name during the client's join request.
A custom server can edit the auto-close and hidden settings, but neither Relay nor Blue objects expose that functionality. Blue Server can create its own channels without depending on a client's join request, though.